Make the SSH port and the global release tests timeout configurables

### Context
The plugin uses default port number when calling ssh commands.
It also uses a hard coded value for global release tests timeout.

### Description
Now, it is possible to configure the port number and the global release tests timeout.

### Example
In pom.xml :
```xml
           <plugin>
                <groupId>net.codjo.maven.mojo</groupId>
                <artifactId>maven-test-release-plugin</artifactId>
                <configuration>
                    <serverMainClass>${serverMainClass}</serverMainClass>
                    <sleepAfterLocalStart>5</sleepAfterLocalStart>

                    <!-- Specify port parameter -->
                    <serverPort>2222</serverPort>

                    <!-- Specify global release test time parameter (in milliseconds) -->
                    <timeout>3600000</timeout>
                    <server>
                    .....
           </plugin>
```

The timeout can also be configured with a textual representation like the following ones :
```xml
<timeout>2 hours 3 minutes</timeout>
``` 
```xml
<timeout>2h 3m</timeout>
``` 
```xml
<timeout>2h3m</timeout>
```